It can sometimes happen that even when using the largest version of a microcontroller for a particular design application there are just not enough I/O port pins to handle all the inputs and outputs. This can be the case when for example several LCDs are driven in parallel or when it is necessary to input values from a large number of switches and pushbuttons. The circuit shown here solves the problem using the I/O port expander IC type MAX7301 from Maxim.